This Application is a U.S. National Phase Application of PCT International Application PCT/JP976/03381.
The present invention relates to the field of diplexers, duplexers, and two-channel mobile communications equipment employed in mobile communications, particularly in mobile phones.
Diplexers employed in mobile communications generally have the configuration shown in FIGS. 9 to 11. Specifically, a diplexer of the prior art has a circuit shown in FIG. 9 which comprises a low-pass filter and high-pass filter formed in a low-dielectric ceramic material as shown in FIG. 10.
In FIG. 10, a conductive layer 24 is formed on a low-dielectric layer 16i as a shield electrode, followed by a laminated low-dielectric layer 16h. Inductor electrodes 23a and 23b are formed on this low-dielectric layer 16h, followed by a laminated low-dielectric layer 16g. A capacitor electrode 22 is formed on this low-dielectric layer 16g, followed by a laminated low-dielectric layer 16f. A capacitor electrode 21 is formed on this low-dielectric layer 16f, followed by a laminated low-dielectric layer 16e. A conductive layer 20 is formed on this low-dielectric layer 16e as a shield electrode, followed by a laminated low-dielectric layer 16d. Capacitor electrodes 19a and 19b are formed on this low-dielectric layer 16d, followed by a laminated low-dielectric layer 16c. An inductor electrode 18 is formed on this low-dielectric layer 16c, followed by a laminated low-dielectric layer 16b. An inductor electrode 17 is formed on this low-dielectric layer 16b, followed by a laminated low-dielectric layer 16a. In the low-dielectric layer 16b, a via hole 25 is formed to create an electrical connection between the inductor electrodes 17 and 18.
Next, FIG. 11 shows a perspective of the diplexer of the prior art. The conductive layers 20 and 24 are connected with end electrodes 26b, 26d, 26f, and 26g at the side of the dielectric substance to form a shielded electrode by grounding the end electrodes 26b, 26d, 26f, and 26g. 
Also, as shown in FIG. 9, a first terminal 907 is formed by connecting an end electrode 26a and the inductor electrode 17 at the side of the dielectric substance, and a first inductor 902 is also formed by connecting the inductor electrodes 17 and 18 through the via hole 25. The end electrode 26a is also connected to the capacitor electrode 19a at the side of the dielectric substance to form a first capacitor 901 between the conductive layer 20. A common terminal 908 is formed by connecting the inductor electrode 18 and capacitor electrode 21 to an end electrode 26c at the side of the dielectric substance. The end electrode 26c is further connected to the capacitor electrode 19b at the side of the dielectric substance to form a second capacitor 903 between the conductive layer 20. This is how a low-pass filter 910 is configured.
Next, a third capacitor 905 is formed with the capacitor electrode 22 facing the capacitor electrode 21 connected to the end electrode 26c. The end electrode 26c is also connected to the inductor electrode 23b at the side of the dielectric substance, and a second inductor 904 is formed by connecting the other end of the inductor electrode 23b to the end electrode 26g. In the same way, the capacitor electrode 22 is connected to the inductor electrode 23a at the side of the dielectric substance, and a third inductor 906 is formed by connecting the other end to the end electrode 26f. The capacitor electrode 23 is also connected to the end electrode 26e at the side of the dielectric substance to form a second terminal 909. This is how a high-pass filter 911 is configured.
Attenuation of the low-pass filter 910 is increased in the passband frequency of the high-pass filter 911, and attenuation of the high-pass filter 911 is increased in the passband frequency of the low-pass filter 910 to ensure mutual isolation.
However, since the number of mobile communications users has rapidly increased in recent years, the trend is towards enabling the use of a system employing two different frequency bands in one piece of communications equipment to make it more likely to secure a communications channel. In this case, a device for dividing two bands is required. If the diplexer of the prior art which comprises a low-pass filter and high-pass filter formed in a low-dielectric ceramic material is used for realizing such a system, due to structural limitations, the higher harmonics cannot be removed. In addition, the size will be larger due to design restrictions.
The present invention offers a small device for dividing two bands and also removing the higher harmonics.
The present invention has a configuration comprising a formed low-dielectric layer and high-dielectric layer. A low-pass filter and an inductor as a matching circuit for the low-pass filter are formed in the low-dielectric layer, and a band-pass filter and a capacitor as a matching circuit for the band-pass filter are formed in the high-dielectric layer.
This configuration allows the present invention to be embodied in a small device which can divide signals input to a common terminal into two bands and remove the higher harmonics.